The present invention relates to a rotary driving device such as a spindle motor or the like for objects to-be-rotated including recording media, e.g., CD-ROMs and MO (magneto-optic) discs, and manufacturing method and device for the rotary driving device.
A spindle motor (an example of the rotary driving device referred to above) is used was a driving device for circular recording media like CD-ROMs, MO discs, etc. The spindle motor is generally a DC type brushless motor and is driven for rotation at a high velocity of several hundreds to several thousands rpm. The spindle motor of this kind includes a turntable for loading a recording medium (an example of the object to be rotated) thereon, and a driving part for rotating the turntable. The driving part comprises a motor frame, a rotor supported to the motor frame in a rotatable fashion, and a stator disposed in the periphery of a rotary shaft of the rotor within the motor frame. The turntable is set integrally with the rotor and a central portion of which has fixed thereon the rotary shaft of the rotor, for example, by way of press-fitting.
The spindle motor is controlled to be driven for rotation at a constant linear velocity (CLV) when driving the CDs or CD-ROMs. Additionally, it is controlled to be rotated with a constant number of revolution (CAV) when driving MO discs.
In manufacturing the above spindle motor, it is important to restrict the vibration of waving of a surface of the turntable within a tolerance zone. The surface vibration in the spindle motor during the rotation leads to a surface vibration of the recording medium, causing a change in distance from a writing and reading head located adjacently to the recording medium, thereby hindering the head from correctly writing and reading to the recording medium. The surface vibration is often due to the press-fitting when the rotary shaft is press-fitted to the turntable or to the assembling of individual components in the spindle motor. More specifically, the surface vibration results, for instance, from a slight difference of the pressing force at the time of press-fitting or a small burr left in a to-be-pressed hole, etc. Therefore, the surface vibration generated during the rotation differs for every spindle motor. The prior art has intended to maintain a high processing accuracy and a high assembling accuracy of each component so as to reduce the above-described surface vibration as much as possible. However, as the processing accuracy and assembling accuracy are enhanced, manufacturing costs are increased thus making the spindle motor expensive.